SOLO time is PIC time and should therefore be logged in the PIC field.
There is no separate field for SOLO time and you should certainly not create a SOLO user definable time field !
PIC time on a single pilot aircraft is considered SOLO, by selecting the SOLO tag from the Type of Operation field :
If the selected logbook has a separate column for SOLO, the software will automatically print the above PIC time in the SOLO column. The PIC column remains empty, unless you select the “Print SOLO also as PIC” checkbox on the Logbook - Logbook Format page.
You can use the pre-coded “Solo” query on the Query page to list all SOLO flights with a single click. This criterion is also available from the Query - Advanced myQuery page.
Continue reading here : Official State Regulations - Recording of Flight Hours